Using a material derived from plants, Penn State researchers have developed a cleaner, more sustainable way to separate and recover dysprosium, a critical rare earth metal used in electronics, engines and clean energy technologies. The approach could help ease supply pressures and reduce the environmental toll of rare earth mining.
A team of Penn State engineers has turned a common plant material into a high-tech tool that could help solve one of the toughest problems in modern manufacturing: how to get critical rare earth metals without wrecking the environment.
By tailoring the structure of cellulose — the main building block of plant cell walls — the researchers created a tiny, “hairy” nanomaterial that can selectively pull out dysprosium, a heavy rare earth element, from mixtures that also contain other metals.
Dysprosium is essential for making semiconductors, high-performance magnets, engines, generators and even components that help keep nuclear control rods stable. It is also in short supply, and current methods of extracting and separating rare earths are energy-intensive, chemically harsh and often polluting.
As demand for advanced electronics and clean energy technologies grows, that pressure is expected to intensify.
“As technology advances, manufacturers will need more and more dysprosium — some forecasts estimate the demand for this material may surge over 2,500% in the next 25 years,” principal investigator Amir Sheikhi, an associate professor of chemical engineering at Penn State and the Dorothy Foehr Huck and J. Lloyd Huck Early Career Chair in Biomaterials and Regenerative Engineering, said in a news release. “Having a sustainable and environmentally friendly way to recover this material will strategically help the U.S. stay competitive with countries like China.”
Rare earth elements are a group of 17 metals that are crucial for everything from smartphones and wind turbines to electric vehicles and military systems. They are often labeled “rare” not because they are scarce in Earth’s crust, but because they are rarely found in concentrated, easy-to-mine deposits. They also tend to occur together and have very similar chemical properties, which makes them notoriously hard to separate.
“Separating rare earth elements from one another has been extremely difficult, due to the metals’ very similar chemical structures,” added Sheikhi, who is also the founding director of the Bio-Soft Materials Laboratory. “We have been looking for a reliable way to separate heavy elements like dysprosium from lighter elements like neodymium, while avoiding the negative environmental side effects that come from current separation approaches.”
Today, most commercial separation methods rely on solvent-based processes that use large volumes of chemicals and sprawling equipment. These systems can require rooms full of machinery and generate significant waste.
Sheikhi’s group took a different route, starting with cellulose, an abundant, renewable material found in virtually all plants. The team modified cellulose at the molecular level to create nanocellulose crystals only about 100 nanometers long — roughly 1,000 times thinner than a human hair.
On each end of these crystals, they engineered dense, hair-like chains of cellulose that carry negative charges. The result is a structure known as anionic hairy cellulose nanocrystals, or AHCNC.
The researchers then tested how this plant-based nanomaterial behaved in a water-based solution containing two rare earth elements: neodymium, a light rare earth used in powerful magnets, and dysprosium, a heavy rare earth often paired with neodymium in high-performance applications.
The separation process relies on adsorption, in which ions from a liquid stick to the surface of a solid. When the AHCNC was added to the mixed-metal solution, the team observed that the “hairs” on the nanocrystals behaved differently than those on other cellulose-based materials they had studied.
In the presence of dysprosium, the chemically modified chains on the nanocrystal ends shrank in a distinctive way, signaling a specific sensitivity to the heavy metal. Further analysis showed that these hairy ends effectively acted like a selective filter, preferentially capturing dysprosium ions over neodymium.
“This is, to my knowledge, the first example of a cellulose-based adsorbent that can selectively filter between heavy and light rare earth elements,” Sheikhi added. “On top of that, our process is very straightforward and efficient. We just add our nanocellulose to a solution and separate the metals.”
Initially, the team expected that the type of chemical groups attached to the cellulose — the so-called functional groups that control how molecules react — would be the main factor driving selectivity. But side-by-side comparisons with other cellulose platforms told a different story.
“After comparing this behavior side-by-side with other cellulose-based platforms, we determined it’s not just the functional group type of the material that facilitates this selectivity,” added Sheikhi. “It’s the structure of the material itself and the position of the functional groups, which showcases the unique properties of these hairy nanostructures.”
That insight points to a powerful design principle: by precisely tuning both the architecture of the nanocellulose and where key chemical groups are placed, engineers may be able to create a family of plant-based filters tailored to different rare earths and other critical minerals.
The work, published in the journal Advanced Functional Materials, builds on Sheikhi’s previous research using cellulose-based compounds to recover neodymium from electronic waste such as recycled computer circuit boards. In the new study, the team extended that concept to dysprosium, demonstrating that a similar sustainable platform can be adapted to target a different, and even more challenging, rare earth element.
Because the new method uses water-based solutions and a renewable, plant-derived material, it has the potential to be cleaner and more sustainable than conventional solvent extraction. The process is also relatively simple, which could make it easier to scale up for industrial use.
With further development, the researchers envision their approach being used to recycle dysprosium and other rare earths from manufacturing scrap, end-of-life electronics and other waste streams. That kind of “urban mining” could reduce dependence on new mining operations and help stabilize supplies of critical materials.
Next, the team plans to test whether their nanocellulose platform can be tuned to isolate additional rare earth elements and other strategically important minerals. They also aim to refine the material’s design and performance with an eye toward scaling the technology for use in factories and laboratories across the United States.
If successful, a plant-based nanomaterial that can cleanly sort out rare earths could offer a rare win-win: supporting the technologies that drive modern life, while cutting down on the environmental costs of the materials that make those technologies possible.
Source: Pennsylvania State University